Niche characteristics of rodents by diverse disturbance in Alashan desert,Inner Mongolia,China

Four diverse disturbance types,namely,farmland,rotationaUy grazed grassland,overgrazed grassland and forbidden grazing grassland,were identified in the Alashan desert region of Inner Mongolia.Rodents were sampled in April,July and October in 2002 and 2003 using the trap-day method.Their spatial and temporal niches among the four disturbance types were assessed using the Shannon-Wiener niche breadth index and the Pianka niche overlap index.The Shannon-Wiener niche breadth index was the highest for Allactaga sibirica and Meriones meridianus (0.925 and 0.908,respectively),intermediate for Cricetulus eversmanni,Phodopus roborovskii and Citellus dauricus (0.789,0.782 and 0.711,respectively),and lowest for Cardiocranius paradoxus (0.003).The Pianka niche overlap indices of six-paired species were the highest and varied from 0.900 to 1.000,suggesting their spatial niche overlapped almost completely.Conversely,the spatial niche overlap index for Meriones unguiculatus,Cardiocranius paradoxus,and Salpingotus kozlovi was zero,thus indicating a complete absence of competition among them.In addition,the temporal niche breadth and overlap indices varied greatly in relation to disturbance types and season.The level of temporal niche overlap in spring and autumn was low while in summer it was high.For all disturbance types and for each season,the temporal niche overlap index of Meriones meridianus and Cricetulus barabansis was always highest but for Meriones unguiculatus and Salpingotus kozlovi always lowest.